JP2651435B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an image processing apparatus used for a facsimile machine or the like.

(Prior Art) In a conventional facsimile machine, when an image, for example, a document including characters and a thin line as shown in FIG. 3 is copied or transmitted, a received image may be partially missing in the thin line as shown in FIG. was there. This occurs because, in the case of a thin line as shown in FIG. 3, the digital signal indicating the gray level of the pixel read by the CCD line image sensor may not reach the slice level as shown in FIG. In this case, although the pixel portion is "black", it is determined to be "white" and the data is omitted.

In order to solve the above-mentioned inconveniences, the conventional facsimile apparatus performs the following correction as a correction for emphasizing fine lines as shown in FIG.

First, as shown in FIG. 5, a 4-bit digital signal indicating the gray level of a pixel of a black point smaller than one pixel is smaller than the slice level as shown in FIG. 4, so that it is passed through a correction filter. Was emphasized. The correction filter performs the correction with reference to the data of the pixels before, after, left and right of the pixel to be emphasized (the pixel indicating the gray level value 6 in FIG. 5). At this time, the emphasis coefficients for emphasizing the pixel levels of the pixels in the main scanning direction and the sub-scanning direction are set and fixed in advance at the time of designing the filter. For this reason, emphasis has been applied even when it is not desired to emphasize the original.

(Problems to be Solved by the Invention) As described above, in the above-described conventional image processing apparatus, the emphasis coefficient for emphasizing the pixel levels of the pixels in the main scanning direction and the sub-scanning direction is preset and fixed. Therefore, it is difficult to arbitrarily change the emphasis coefficient with respect to the pixel levels of the pixels in the main scanning direction and the sub-scanning direction.

Accordingly, it is an object of the present invention to provide an image processing apparatus that eliminates this problem and can arbitrarily change the enhancement of the pixel level of a pixel of interest in the main scanning direction and the sub-scanning direction.

[Configuration of the invention]

(Means for Solving the Problems) The present invention relates to an image processing apparatus for correcting the pixel level of a target pixel by referring to the pixel levels of reference pixels before, after, left and right of the target pixel. About 2
A value obtained by incorporating the enhancement coefficient into the secondary differential output is calculated based on the secondary differential output, the secondary differential output relating to the reference pixel in the horizontal direction, and the respective enhancement coefficients, and this value is used as the pixel level of the target pixel. The correction is performed to enhance the pixel level of the target pixel, and the enhancement coefficient is independently changed in the front-rear direction and the left-right direction.

(Operation) In the present invention, a value obtained by incorporating the enhancement coefficient into the secondary differential output is calculated based on the respective secondary differential outputs and the respective enhancement coefficients for the reference pixel in the front-rear direction and the horizontal direction of the target pixel. Then, by taking this value into the pixel level of the target pixel, a correction for enhancing the pixel level of the target pixel is performed. The emphasis coefficient can be changed independently in the front-rear direction and the left-right direction.

That is, in the present invention, the scanning direction is X, the image signal at X is f (X), and the f (X) is sampled in units of one pixel, and continuous pixel levels are _Xm-1 , _Xm , _{Xm. If you +1}
The primary differential output and the secondary differential output are f ′ (X _m ) = X _{m + 1} −X _m (1) f ″ (X _m ) = X _{m + 1} + X _m−1 −2X _m. 2) given by

In the present invention, f ″ (X _m ) is multiplied by a coefficient and
Fine line emphasis is performed by subtracting from (X _m ).

Now, when the pixels are arranged as shown in FIG. 2, the secondary differential output in the main scanning direction for enhancing the pixel B to the pixel B 'is f "(X) = A + C-2B... (3) and the secondary differential output in the sub-scanning direction is f ″ (Y) = D + E−2B (4)

Assuming that the enhancement coefficients in the main scanning direction and the sub-scanning direction are α and β, the enhancement output B ′ is B ′ = B− {α (A + C−2B) + β (D + E−2B)} (5)

As described above, the pixel B is emphasized by performing the calculation of the equation (5).

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention, in which one-line delay units 2, 3 and one-bit delay units 4,
5,6 and 7, subtractors 8,9,10,11 and 17, adders 12,14
And 16, and multipliers 13 and 15.

The operation of this embodiment will be described for the case where an image as shown in FIG. 2 is input.

First, focusing on the sub-scanning direction, a digital signal (hereinafter, referred to as a signal D) indicating the gray level of the pixel D is input to the input line 1. Subsequently, at the time of scanning the next line, digital signals (hereinafter, referred to as signal A, signal B, and signal C) indicating the gray level of the pixels A, B, and C are sequentially input. At this time, the signal D is shifted by one line through a one-line delay unit. Further, at the time of scanning the next line, a digital signal (hereinafter, referred to as signal E) indicating the gray level of the pixel E is input. At this time, the signal D sent from the one-line delay unit 2 is further shifted by one line through the one-line delay unit 3, and the signals A, B and C are shifted by one line delay unit 2.
Are shifted by one line.

Next, focusing on the main scanning direction, the signal A is first transmitted from the one-line delay unit 2, and then the signal B and the signal C are output.
Are sent out in this order. The signal A passes through a 1-bit delay 5
Bit shifted. Next, when the signal B is transmitted, the signal B is shifted by one bit by the one-bit delay unit 5 at this time. At this time, the signal A is further shifted by one bit through the one-bit delay unit 6.

The signal input to the input line 1 is shifted by one bit by a one-bit delay unit 7 and is applied to a subtractor 8.
The signal B output from the bit delay unit 5 is applied to subtracters 8, 9, 10, 1
The signal A output from the 1-bit delay unit 6
Is applied to a subtractor 9, the signal C output from the one-line delay 2 is applied to a subtractor 10, and the signal D output from the one-bit delay 4 is applied to a subtractor 11.

The subtractor 8 subtracts the signal B from the signal E (E−
B) is executed, and the calculated value is added to the adder 14. The adder 9 performs an operation (A−B) of subtracting the signal B from the signal A, and adds the calculated value to the adder 12. Also subtracter 10
Performs an operation (CB) for subtracting the signal B from the signal C, and adds the calculated value to the adder 12. The subtracter 11 performs an operation (DB) for subtracting the signal B from the signal D, and adds the calculated value to the adder 14.

The adder 14 adds the calculated value of the subtractor 8 and the calculated value of the subtractor 11, executes an operation (D + E-2B), and adds the calculated value to the multiplier 15. The adder 12 performs an operation (A + C−2B) by adding the calculated value of the subtractor 9 and the calculated value of the subtractor 10, and adds the calculated value to the multiplier 13.

The multiplier 15 multiplies the calculated value of the adder 14 by an enhancement coefficient β in the sub-scanning direction given from the outside.
Perform -2B). The multiplier 13 executes an operation α (A + C−2B) for multiplying the calculated value of the adder 12 by an externally applied enhancement coefficient α in the main scanning direction.

The calculated value of the multiplier 15 and the calculated value of the multiplier 13 are
, And the calculated value of the adder 16 is added to the subtractor 17, and the subtractor performs an operation of subtracting the calculated value of the adder 16 from the value B. Eventually, the value B- {α (A + C−2B) + β (D + E−2B)} shown in the above equation (5) is calculated from the subtractor.

Thus, in this embodiment, since the circuit configuration is as described above, the emphasis coefficients α and β can be arbitrarily changed.

By the way, when a manuscript or the like in a newspaper place is emphasized, a small variation in the ground part is amplified and black noise is likely to appear. Also, in the halftone mode, if the character or the like is emphasized too much to make it clear, the halftone level part becomes unnatural. However, this problem can be solved by switching between the time when the enhancement coefficient is applied (when the value is increased) and the time when it is not applied (when the value is reduced).

〔The invention's effect〕

As described above, the present invention calculates a value obtained by incorporating the enhancement coefficient into the secondary differential output based on the secondary differential output and the respective enhancement coefficient for the reference pixel in the front-rear direction and the horizontal direction of the target pixel. Calculated, and by taking this value into the pixel level of the target pixel to perform correction to emphasize the pixel level of the target pixel, and to change the enhancement coefficient independently in the front-rear direction and the left-right direction, Desired enhancement can be performed in the front-rear direction and the left-right direction. Further, there is an advantage that the image quality can be improved by applying to a manuscript of a newspaper place and a halftone mode.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention, FIG. 2 is an explanatory diagram for explaining an operation of decomposing an image into pixels in the present embodiment, and FIG. FIG. 4 is an explanatory diagram for explaining a received image when a thin line is copied or transmitted using the image processing device of FIG. 4, FIG. 4 is a diagram showing a gray level and a slice level of a pixel, and FIG. FIG. 1 ... input line, 2 ... 1 line delay, 4, 5, 6, 7 ... 1
Bit delay unit, 8, 9, 10, 11, 17 …… Subtractor, 12, 14, 16 ……
Adder, 13,15 ... Multiplier, 18 ... Output line.

Claims (1)

(57) [Claims] 1. An image processing apparatus for correcting a pixel level of a target pixel by referring to pixel levels of reference pixels before, after, left and right of the target pixel. Based on the secondary differential output relating to the reference pixel and the respective enhancement coefficients, a value obtained by incorporating the enhancement coefficient into the secondary differential output is calculated, and this value is incorporated into the pixel level of the pixel of interest, thereby obtaining the pixel of interest. An image processing apparatus for performing a correction for emphasizing the pixel level, and changing the emphasis coefficient independently in the front-rear direction and the left-right direction.